1. Field of the Invention
The present invention relates generally to the art of adjustable-length columns, such as those used with chairs, stools, tables and the like. More specifically, the present invention relates to a technique for mounting the washer plate to the hub tube, the plate in turn receiving the outer end of the piston rod of a gas spring. The technique facilitates assembly and increases the strength of the washer plate securement. Still more specifically, the present invention relates to securing a washer plate into the lower end of an expanded cross-section hub tube and providing an expanded surface area on the tube for attachment of the legs of the chair or table.
2. Description of the Prior Art
Adjustable-length columns for chairs, tables and the like have been known for many years. For example, Wirges U.S. Pat. No. 4,245,826 issued Jan. 20, 1981 for "Resilient Column Of Adjustable Length" discloses a column including a pneumatic spring of the piston-and-cylinder type. The piston rod of the cylinder extends downwardly and is affixed to a washer located at the lower end of the tube. Upward movement of the washer into the tube is prevented by an indentation just above the lower end. The washer is confined between the indentation and an inwardly directed flange created by rolling the end of the tube inwardly so that the end faces are substantially parallel to the axis of the tube. The upper end of the cylinder is appropriately mounted in a guide tube for sliding upward and downward movement with respect to the lower end of the tube, so that the height of chairs, chair seats, tables or the like can be adjusted.
U.S. Pat. No. 3,711,054 was issued Jan. 16, 1973 to Fritz Bauer for "Continuously Adjustable Lifting Devices". This early patent also discloses a technique for providing stepless height adjustment of the seat of a chair, stool or the like using a fluid spring. The end of the piston rod in this device is held in the lower tube by providing an inwardly flanged rim and a disc-shaped body of yieldably resilient material. The body is arranged between two metal washers to confine the body against the flange and prevent upward or downward movement of the end of the piston rod relative to the lower tube.
A wide variety of modifications of basic column design are disclosed in the prior art. For example, in Bauer, et al. U.S. Pat. No. 4,969,619 issued Nov. 13, 1990 for "Adjustable-Length Columns For Chairs, Tables Or The Like", the attachment technique for the washer is modified by rolling the end of the tube further, so that the end face points upwardly and in direct contact with the bottom of the washer. In this device, the washer is held in place against a plurality of indentations by the end face of the tube. It is suggested in the Bauer, et al. patent that such further rolling of the end of the tube provides additional strength when compared to the Wirges design.
Another technique for mounting chair seats to supports is shown in Collier U.S. Pat. No. 1,399,464 issued Dec. 6, 1921 and entitled "Chair Iron". In this design, the seat is held against the tube by a bead above and below the upper plate of the support, each of the beads extending outwardly from the generally cylindrical spindle.
Other patents which disclose various techniques for holding components of shock absorbing devices, including piston rods, are U.S. Pat. No. 4,913,268 issued Apr. 3, 1990 to Parker, et al. for "Weldless Automotive Shock Absorber"; U.S. Pat. No. 5,353,898 issued Oct. 11, 1994 to Handke, et al. for "Vibration Damper Unit"; and U.S. Pat. No. 4,480,730 issued Nov. 6, 1984 to Koller, et al. for "Shock Absorber Unit For Vehicles".
A relatively common technique still used for attaching the washer to the hub tube is a 360.degree. MIG weld around the perimeter of the washer. While this technique has been found entirely suitable from a strength standpoint, the process is time consuming and expensive.
While some manufacturers have eliminated such welding by using the indentation techniques mentioned above, the shelf formed inwardly of the washer is quite small relative to the ID of the main body of the tube. This is especially true where indents, rather than an inwardly directed flange, are provided. Some current designs contain as few as six indents and, under relatively low loads, the washer can be pushed past them and into the tube.
Another aspect of the construction of seating devices using such adjustable-length columns is attaching legs to the tubes. In most cases, such attachment is provided by welding both the horizontal and vertical surfaces of the legs to the small hub tubes. This is due primarily to the relatively small O.D. of the lower end of the tube compared to the size of the inner ends of the legs.
A significant advance in this art would result from a simplified technique for attaching the washer to the lower end of the hub tube and facilitating attachment of chair legs to the tube of adjustable length columns by providing a larger outer surface for such tubes.